This invention relates to an improved photographic method for making screen structure for a cathode-ray tube (CRT).
It is known to make a screen structure, such as a black, light-absorbing matrix, or a luminescent layer, by a photographic method. The use of an IC filter with a tailored light transmission to adjust the light intensity across a projected light field in such method is also known. Such intensity-correction (IC) filters have been made of custom-ground glass, of a layer of vapor-deposited metal particles, of a layer of silver particles in gelatin, or of a layer of carbon particles in gelatin, as disclosed for example in U.S. Pat. Nos. 3,420,150 to S. H. Kaplan, 3,982,252 to E. Yamazaki et al., 3,582,326 to H. E. Smithgall and 3,592,112 to H. R. Frey respectively.
While each of these prior types of IC filters is useful, nevertheless they are difficult and relatively expensive to reproduce reliably, thus adding to the cost of equipping a manufacturing facility. The latter three types are comprised of a layer of opaque particles in varying densities and/or varying layer thicknesses. When the particles are relatively large and/or the layers are relatively thick, the filter produces an undesirable amount of light scattering, degrading the quality of the screen structure being made. Light scattering can also be caused by scratches, pinholes, bubbles and other defects in or on the layer. The latter two types, which use organic binders, are somewhat easier and cheaper to reproduce reliably than the former two types, but nevertheless frequently have pinholes, bubbles and such light-scattering defects. Also, the latter two types have poor abrasion resistance and are easily damaged with normal handling in the CRT factory.
Light filters with substantially uniform light transmission and made of a cermet layer are also known, as disclosed in H. R. Zeller et al., J. Applied Physics 44 (1973) 2763-2764; and R. W. Tokarsky et al, J. Vacuum Science Technology 12 (1975) 643-645. The cermet layer comprises opaque inorganic metal particles in a transparent inorganic medium. Such cermet layers may be made by vaporizing, as by evaporating or sputtering, the desired materials and then depositing the vaporized materials on a support surface. Such cermet layers are intended to have a substantially uniform light transmission across their surfaces. If the light transmission is nonuniform, it is not by design, not tailored for a particular purpose and, therefore, not easily and reliably reproducible. Such cermet layers can be made with very small-sized particles in very thin, dense, smooth-surface layers that are relatively free of fabrication defects, are resistant to damage by abrasion, and exhibit relatively low light scattering.